Testing apparatus with sound absorbing panels forming air passages



Aug. 15, 1950 T. T. TUCKER 2,519,160

TESTING APPARATUS WITH SOUND ABSQRBING PANELS FORMING AIR PASSAGES Filed Dec. 5, 1942 4 Sheets-Sheet l INVENTQIB THOMAST. UCKER.

ATTORNEY Aug. 15, 1950 2,519,160

T. T. TUCKER TESTING APPARATUS WITH SOUND ABSORBING PANELS FORMING AIR PASSAGES Filed Dec. 5, 1942 4 SheetsSheet 2 INVENTOR. THOMAS T.TUCKER.

Aug. 15, 1950 TI "r. TUCKER TESTING APPARATUS WITH SOUND ABSORBING PANELS FORMING AIR PASSAGES 4 Sheets-Sheet 3 Filed Dec. 5, 1942 INVENTOR THOMAS T. TUCK ER,

flu. 6mm

ATTORNEY b .E I

T. T. TUCKER ARATUS Aug. 15, 1950 2,519,160 TESTING APP WITH SOUND ABSORBING PANELS FORMING AIR PASSAGES 4 Sheets-Sheet 4 Filed Dec. 5, 1942 FIGJL T. Y mm m w EA v T mM M 0 H Patented Aug. 15, 1950 TESTING APPARATUS WITH SOUND ABSORBING PANELS FORMING AIR PASSAGES Thomas T. Tucker, Atlanta, Ga., assignor to Belle Weather Incorporated, Atlanta,

tion 01' Georgia Ga., a corpora- Application December 5, 1942, Serial No. 467,963

5 Claims. 1

This invention relates to structures wherein tests may be carried out in connection with various apparatus, for example, motors, and driven devices, such as propellers for airplanes and other high speed devices, whereby certain conditions or characteristics thereof, including fuel consumption, temperature of oil and operation of parts and size and pitch of propeller blades, are to be investigated or determined. The invention lends itself for other applications where it is desirable to absorb or reduce noise.

In structures for carrying out tests in connection with engines and propellers for airplanes, difficulty has been experienced in attaining satisfactory results, since the sound absorbing material, so far as I have knowledge, lacked eflicient sound absorbing capacity and would not withstand the vibrations setup except for a limited period; in some instances the material would become matted and in other instances it would absorb moisture and oil or gases in the oil. Some materials would be materially affected by the use of cleaning solutions or by water due to rain fall or cleaning. It was frequently impractical to use fibrous materials because their shoft fibers could not be retained in position, but would escape and pollute the air stream. Cleaning was a laborious task and often made the material unsatisfactory for use. Various detrimental conditions developed due to contact of these materials with metal. Where cast stone was employed, cracking at the mortar joints would develop.

One object of the invention is to provide an improved structure of this character having a plurality of sound absorbing units which may be readily fabricated and economically assembled.

Another object of the invention is to provide a structure of this character having sound absorbing units ofan efficient capacity for absorbing sounds of high intensity and capable of withstanding vibrations due to high air velocities, eddy currents and complex sound patterns.

Another object of the invention is to provide an improved structure of this character havin sound absorbing units which are fire-proof, are not affected by climatic conditions, resist the deleterious effects of water, oil, gasoline vapor, water vapor and other precipitated matter and chemicals of various kinds, whereby various cleaning fluids and materials may be applied to remove the accumulated matter, and is self draining when subjected to rain fall.

Another object of the invention is to provide an improved structure of this character having sound absorbing unit which may be readily cleaned to remove accumulations of oil, grease or other material to eliminate fire hazards and to maintain eflicient sound absorbing conditions.

A further object of the invention is to provide an improved structure of this type having sound absorbing units wherein the sound absorbing material, which may be of any predetermined density, may be subjected to sound vibrations of various intensities and frequencies as well as vibrations caused by high wind or air velocities, without affecting its density, structural strength and stability, whereby both durability and efficiency result.

A further object of the invention is to provide an improved sound absorbing unit employing a material which is impervious to water, oils, grease and various kinds of chemicals, has a high capacity to absorb sound and structural characteristics capable of withstanding compressive impacts due to vibrations resulting from sound producing or air circulating means and of being supported and retained in acoustical relation to the sound producing means, whereby pollution 01' the air stream is prevented.

A further object of the invention is to provide an improved structure of this character having sectional sound absorbing units, whereby the sections may be pre-fabricated ready for assembly and each replaceable in the event of damage.

A further object of the invention is to provide a testing structure having related sound units each adjustably connected to the walls, floors or ceilings thereof to compensate for disalinement or uneven surface conditions on said walls, floors or ceilings.

A still further object of the invention is to provide an improved structure of this type having simplified connections between the sound absorbing panels or units and between the latter and the walls, floors or ceilings of the structure to insure ready assembly or installations and repairs Or replacements.

Other objects of the invention will be apparent to those skilled in the art to which my invention relates from the following description taken in connection with the accompanying drawings, wherein Fig. 1 is a perspective view diagrammatically showing a testing structure embodying my invention.

Fig. 2 is a perspective view of a testing structure showing a modified form.

Fig. 3 is a perspective view of a frame forming part of a sound absorbing panel.

Fig. 4 is a view similar to Fig. 3 but showin a modified form of frame.

Fig. 5 is a fragmentary elevational view of one of the units, wherein the long sides of each panel are disposed horizontally, parts being broken away.

Fig. 6 is an eevational view of one of the units, wherein the long sides of each panel are disposed vertically, parts being broken away.

Fig. 7 is a fragmentary end elevation of a battery of units mounted on a beam above the fiooring of the structure, where units are parallel to the same axis.

Fig. 8 is a fragmentary plan view showing a battery cf units having a modified arrangement thereof wherein certain units ar parallel to one axis and other units are parallel to a different axis.

Fig. 8a is a fragmentary section on the line 808a of Figure 8, enlarged (the view being foreshortened).

Fig. 9 is a section on the line 9-9 of Fig. 5, enlarged (the view being foreshortened).

Fig. 10 is a section on the line llll0 of Fig. 5, enlarged (the view being foreshortened) Fig. 11 is a fragmentary perspective view of one of the panels, enlarged.

Fig. 12 is a fragmentary section of parts illustrated in Fig. 9, enlarged; showing the mounting of aunit on a flooring or wall.

-' Fig. 13 is a fragmentary section similar to Fig. 12, but showing the mounting of a unit on a sill which is to be supported on a beam.

. form of bracing between the units.

Fig. 17 is a fragmentary section showing modified form of the connection between adjacent panels and the bracin devices for a unit.

Figs. 18, 19 and 20 show modified arrangements for connecting the panels of a unit.

In the drawings, 1 indicates as an entirety a structure or building (shown substantially diagrammatically) having related walls arranged to provide an inlet end and an exhaust end, each wall being formed of suitable material. 2, 2 'indicate batteries or sets of sound absorbing units each of sectional or panel construction, as later set forth, these batteries or sets being spaced to provide between them a tunnel-like section I within the structure to accommodate the apparatus or device A to be tested. In the form of construction shown in Fig. 1, the structure I consists of a floor or foundation la, side walls lb and a ceiling lc, open at its opposite ends, the batteries or sets of units 2, 2', being mounted within these walls and ceiling adjacent to such ends. Fig. 2 illustrates substantially diagrammatically a modified form of structure lat, wherein one end (for example, the inlet end) has a vertical member Ix in which a battery of units 2 is mounted; but it will be obvious that both ends of the structure may be provided with vertical members lat, each enclosing and supporting a battery of units. It will be understood that the apparatus A to be tested is suitably mounted on the flooring la or otherwise, so as to absorb all mechanical vibrations incident to the operation thereof to eliminate transmission of these vibrations to other parts of the structure; also, either end of the structure may constitute the intake end or exhaust end, this in some instances depending upon whether a pressure propeller or draught propeller is employed. The units of the batteries 2, 2', are preferably similar in construction, so that reference to one battery will suffice for both. As shown, in Figs. 1, 2, 5 and 6, the units of each battery are disposed in parallel relation, spaced to insure movement of the air through the sound absorbing material. By preference, this spacing is approximately 22" measured from center to center, although such spacing may be increased or decreased to meet specified conditions. While this parallel relation is preferable, conditions may make it desirable to improve the efficiency of the structure to position the units in a different relation, whereby a turbulence may be created in the air stream. Each unit, indicated as an entirety at 3, may consist of one or more panels 3' depending upon the area or space in the structure provided for the panels and other conditions, but preferably, as disclosed herein, I provide for plural-cell panels, as will be apparent from Figs. 3 and 4. Each panel 3' is preferably of rectangular shape and consists of a frame having side bars Q and end bars 5 with an intermediate connecting member 6 for dividing the panel frame into separate cells, spaces or areas which are filled with the sound absorbing material I (later referred to). The connecting member 6 may be omitted when desired. The opposite ends of the side bars A are suitably secured to the adjacent ends of the end bars 5. The member 6 may be U-shaped or I-shaped in cross section. The walls i, 5, are preferably U-shaped in cross section to permit the ready assembly of the panels in allned relation into a complete unit free'of protuberances and mounting of the unit in fixed relation to the flooring or other support and walls of the structure, as well as disassembly and replacement, as later set forth. Where sheet metal is available, the bars 4, 5 are formed from rolled metal stock U-shape in cross section. As shown in Fig. 3, the intermediate member 6 extends longitudinally of the panel 3, whereas in Fig. 4 the intermediate member 6 is disposed transversely. The material 1 is covered or faced on both sides thereof with foraminous sheetings 8, such as expanded sheet metal rolled fiat (as shown in the drawings), or welded or woven wire, providing in each sheet throughout its area a plurality of relatively small openings. The openings in each sheeting may be of a size to expose approximately 30% of the area of the sound absorbing material in each panel. The sheetings 8 lap over the opposite outer faces of the side walls of the frame bars 6, 5, and are preferably secured thereto by welding, screws or other suitable devices, such overlapping serving to reinforce the side walls of the frame bars 4, 5. This reinforcing arrangement is highly advantageous since the panels may be fabricated at the factory and shipped to the place of installation and handled without danger of the side walls 4, 5, being deformed or distorted. The employment of panels frames having U-shaped or channeled side and end bars provides for the use of simplified mounting devices for each unit with respect to the walls of the structure I and simplified connecting devices between the panels of each unit, the devices preferably having a standardized shape, rolled or formed from sheet metal stock, which may be readily cut to desired lengths and assembled, and having walls which may be readily secured to the external surfaces of the sheetings 8.

As shown in Fig. 5, the panels 3 may be disposed so that their long sides extend horizontally, whereas in Fig. 6 the panels 3' are shown with their long sides extending vertically.

The sound absorbing material 1 employed by me embodies-characteristics peculiarly adapted for testing structures of the type herein referred to, to efliciently meet the problems and conditions involved. The material consists of fiber glass, that is, pure glass in fibrous form, the fibers being intermingled into a mass forming throughout the area of each panel or cell a labyrinth of minute air spaces between them when placed within the panel or cell between the sheetings 8. As the sheetings on both sides of each panel are formed with openings and the entire area therebetween is filled with fibrous glass, the latter provides a filtering media for the passage of sound waves in either direction through the panel. Glass is relatively high in tensile strength, which insures stability of the fibrous mass. The material may have any predetermined den ity throughout its area, and held in position by the pressure of the sheetings thereon to avoid danger of matting or settling of the material, or becoming deformed or disintegrated irrespective of impacts on the material due to complex sound vibrations, wind or eddy currents, or air pressure of varying millibars, it being obvious that the greater the density of the fibrous material the greater will be the pressure exerted by the sheetings thereon. It will thus be observed that due to this stabilized condition of the material 7, its filtering characteristic and its maintained positioning between the sheets, as above set forth, it is not only effective for deadening sounds of varying intensities for each test, but permits successive tests to be made under like conditions. By preference, the fiber glass is loosely packed in the panels or cells for sounds having a high frequency and heavily packed in the cells for lower sound frequencies. Also, by using relatively thin flat sheet metal for the sheetings, as shown in the drawings, I am enabled to form therein open ings of relatively small size to prevent the longer fibers of the homogeneous mass from being sucked therethrough. Furthermore, fiber glass is fire-proof so that danger of fire resulting from oil, gasoline, vapor and water vapor is avoided and it is also capable of withstanding deleterious effects or chemical reaction from ingredients in these and other chemicals, since hydrofluoric acid is the only acid known capable of attacking glass, so that any desired kind of cleaning material or solution may be used to remove accumulations on the material without danger of affecting its sound absorbing qualities; likewise, this material is not affected by contact with metal, which permits it to be supported in direct contact with metal walls and fiat sheetings 8 (as already set forth) or by exposure to climatic conditions and being nonhygroscopic the material does not absorb water, so that when the material is subjected to rain the water readily drains out and very little moisture is retained in the material. In addition to these stable mechanical qualities, which insures durability this material has an unlimited compressibility and flexibility which permit it to be subjected to loads or impacts of varying intensities due to sound vibrations induced separately or in complex patterns or wind and air velocity without danger of affecting its sound absorbin quality. It will be observed therefore that the impacts on the material whether induced by sound, as in the testing of an engine, or induced by air circulation, as in the testing of a propeller or other driven device, will not affect its stable or physical condition or its sound deadenin capability or its position between the sheetings 8.

Tests made by me of fiber glass between sheetings, as above set forth, under actual operating conditions show sound deadening properties exceeding approximately 50 decibels, which is a substantial increase of sound deadening properties of fiber glass in this form over other materials, which increase I attribute to the inert chemical characteristics of fiber glass and its tensile strength and mechanical stability plus the physical relationship of its fibers whereby numberless minute air areas are formed between them.

Also, in addition to the above characteristics, this kind of sound absorbing material being exceedingly light in weight, the panels are readily handled when bein assembled to provide large units.

It will be observed that each of the bars 4, 5, which form the frame for each panel 3', is of a shape in cross section (that is, provided with angularly related walls) which facilitates its alinement with the adjacent bar of an adjoining panel, and with the mounting or securing devices on the fiooring la, the side walls lb or the ceiling lc. For example, in Figs. 9 and 12 the side walls 4' of the bars 4 are parallelly related and extend outwardly. This arrangement permits the walls 4' of the bottom bar 4 on the lower panel 3' to fit over correspondingly related side walls 9 to a channel member 9', the bottom wall of which rests face-to-face on the flooring or concrete base la, to which the channel member 9 may be secured by a suitable bolt ID. The side walls 9 terminate in inturned flanges 9' on which the bar 4 rests, these flanges serving to reinforce the side walls 9, whereby the latter may carry the weight of the adjacent unit 3. The side walls 4 of the bar 4 may be suitably secured to the side walls 9, preferably by screws H, which secure the parts rigidly together to eliminate rattling and maintain the side walls 9 in vertical position. The upper bar 4 for the panel 3 adjacent the ceiling is telescopes into an inverted U-channel memher [2, the bottom wall of which engages faceto-face with the ceiling (9, to which the member l2 may be secured by a bolt [3. As shown, the side walls l2 of the member [2 slidably fit the outer faces of the panel sheetings 8, to which they may be secured by screws I4. This construction of the bars 4 permits the side walls 4' of the bars 4 of adjacent panels to be mounted edge-to-edge, whereby they may be welded, as shown in Fig. 19; also, where it is desired to provide substantially continuous sound absorbing surfaces the bars 4 may be reversed, as shown in Fig. 18, and their main walls related face-to-face, whereby they may be welded together. The construction also provides for the employment of U-channel members 15 between the adjacent bars 4 of adjoining panels 3 (see Fig. 9), the bottom wall of the channel member being in face-to-face relation with the bottom wall of the bar 4 for one panel 3' and the side walls I5 of the channel member having face-to-face relation with the side walls 4 of the adjacent bar 4 and overlapping face-to-face relation with the side walls 4' of the adjacent bar 4 for the adjoining panel 3', whereby each side wall l5 may be secured to the adjacent side wall 4' by a screw 16. By preference, one screw l6 extends through and clamps one side wall 15 7 to the side wall 4' of the bar 4 of one panel and another screw l extends through and clamps the other side wall IE to the remote side wall 4 of the bar 4 of the adjoining panel, so that the two panels 3' are held in alined relation and against lateral movement. In this form of construction, the lowermost panel 3' is supported perpendicularly to the floor la and the upper panels are alined therewith to form a vertically disposed sound absorbing unit.

Where each unit comprises two or more vertical tiers of panels 3', the marginal ends of the sheetings 8 on each panel 3 preferably extend beyond the side walls 4' of the frame section 5 at one end of the panel and at its opposite end these marginal ends of the sheeting 8 terminate at a point remote from the free edges of the side walls 5' of the adjacent frame end bar 5, so that when the panels 3 are assembled the sheetings 8 on one panel overlap the side walls 5 of the frame bar 5 of the adjoining panel and are secured to the latter side walls by screws H, as shown in Fig. 10.

By preference, the openings in each panel 3' for the screws ll, l5 and H are formed therein at the factory and in making assembly of the panels, these openings are then utilized to mark the locations of the screw openings in the channel members 3', l5 and walls l2, which latter openings are then drilled and tapped to receive the screws. This arrangement permits the units to be readily related and removably secured to floors and ceilings having uneven portions in andthroughout their areas.

By preference the front or leading edge of each unit is provided with a nose member i8 (see Fig. 10) having a rounded front wall IS. The sides l3" of the member l8 ma be secured by screws l9 to the sidewalls 5' of the end bars 5. The nose member l8 and paneled unit may be reinforced by an upright member 20, preferably of U-shape in cross section and preferably secured to the floor la by an angle 2l suitably bolted to the member 20 and flooring la and also preferably secured to the ceiling lc by an angle 22 suitably bolted to the member 20 and ceiling lc, as shown in dotted lines (Fig. 10)

Also, by preference, the rear edge of each unit is provided with a tail member l8:c (see Fig. 10) having side members lBm', which may be secured to the side wall 5' of the adjacent bar 5 by screws l8a, and outer walls l8a: being disposed in converging relation to provide stream-line terminating walls for each unit 3.

23 indicates connections between the units 3 which may be desirable under certain conditions. Each connection 23 consists of a sheet metal member having a wall 23' spanning the space between adjacent units and depending side walls 23" which may be secured to adjacent panels by screws. The connections 23 may be located substantially midway between the flooring la and ceiling lc substantially in line with the joints between adjacent panels and secured thereto by the screws l5, as shown in Figs. 9 and 16, or intermediate the upper and lower frame bars of alined panels 3' and secured to the latter by screws l6, as shown in Fig. 15. A connection 23 also serves to connect the outer unit 3 to the adjacent side wall lb (Figs. 15 and 17) or upright wall lb' (Fig. 7), the outer side wall 23" of the connection being secured by a bolt 24 to the wall. The connections 23 may consist of a plurality of relatively narrow metal strips spaced from end to end of the units or a continuous channel shaped member substantially equal in length to the units. In this latter form of construction the connections serve as a platform for an operative while inspecting or cleaning the panels. When the connections comprise spaced strips, boards may be laid thereon to serve as platforms. Where it is desirable to reinforce the connection of the outer unit 3 with the adjacent wall lb, I may provide within the bars 4 a channel member 25 (shaped in cross section to fit the walls thereof) in lieu of a U-member l5, and secure the side members 23" and side walls 4' together b a bolt 25, as shown in Fig. 17.

Figs. '7 and 13 illustrate a modified arrangement wherein the battery of units is mounted above the floor I a. In this form of construction I may provide a plurality of cross beams 27 (one only being shown) suitably supported at their opposite ends in the walls lb or other supporting means lb (Fig. 7) within the building I and mount thereon sills 28, one for each unit, to which the channel member 9' are secured by bolts III, as shown in Fig. 13.

Figs. 8 and 8a illustrate a modified arrangement of units 3. In this form of construction, I provide sets of units 2a, 2b, 2b, between side walls lb, the set of units 2a being at the engine end of the structure I and disposed parallel to the direction of air flow as indicated by the arrow :1: and the sets of units 2b, 2b, being mounted rearward of the units 2a. As shown, the units 2b are parallel to each other but inclined relative to the units 2a, whereas the units 2b are similarly related to each other but inclined in an opposite direction to the units 2b. In this arrangement portions of the sound absorbing material are positioned in the path of the moving air to insure impact of the vibration set up in the air with the material. Each unit of each set may be mounted on the flooring as shown in Fig. 12. By preference, the outer units of each set 212, 2b, are connected to the side walls lb by connections 23; also these units may be connected by connections 23', along or adjacent their opposite ends in the manner alread set forth. By preference, I provide between the units of the set 2a, horizontally disposed sound absorbing units 25, preferably spaced one above the other approximately 24" measured from center to center. In this arrangement the bars 4 for each unit 25 are reversed so that main walls thereof engage the opposite outer faces of the sheetings 8 of the adjacent vertical units 2a (see Fig. 8a). Also in this arrangement the sheetings on the lower sides of the units 25 are provided with extended laterally bent end portions 8a, which are bolted to the adjacent unit 2a.

Fig. 20 is a fragmentary view showing two alined panels, wherein the side walls 4' of the bars 4 engage edge to edge, but the sheetings 8 on the upper panel bar 4 overlap the side walls 4' of the lower panel frame bar 4 and are secured thereto by screws 26.

From the foregoing description it will be observed that the construction of the frames for each panel provide for the ready assembly of the panels one with another side by side and end to end and ready mounting on the floor and connection with the side walls and ceilings and that complete installation may be made without danger of mutilatz'ng or distorting the sound absorb,- ing material or the sheetings therefor. Accordingly, the panels may be fabricated at the factory ready for assembly. Likewise, one or more panels may be removed and others substituted in a ready manner, since all parts may be removably related into complete units.

It will be understood that the frame bars permit the panels to be mounted in end to end or side by side relation into a complete unit so that welding or connections between them may be omitted; however, this relation of the bars permits adjoining frame bars to be connected together when desired, as hereinbefore set forth.

As already set forth, the structure I is shown diagrammatically merely for illustrative purposes, but in practice provision is made for the installation and removal of the apparatus to be tested.

To those skilled in the art to which my invention relates many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. My disclosures and the description herein are purely illustrative and are not be in any sense limiting.

What I claim is:

1. In testing apparatus, the combination with a structure having a support and spaced side walls, of a battery of units between said side walls disposed side by side in spaced relation to form flow paths for a, sound carrying medium, each unit comprising a plurality of alined panels, each consisting of a skeleton frame the sides of which removably engage the sides of adjacent frames, foraminous sheetings secured along their marginal portions to the opposite sides of said frame and a homogeneous mass of substantially chemically inert, non-hygroscopic, incombustible, shock resistible fibrous material uniformly filling the area between said sheetings, the lower side of the frame for the lower panel consisting of a U-shaDed member the side walls of which extend downwardly, and a channel member fixed to said support removably fitting into said U- shaped member.

2. In testing apparatus, the combination with a structure having a support, a ceiling and spaced side walls, of a battery of units mounted on said support between said side walls and disposed side by side in spaced relation to form paths for a sound carrying medium, each unit comprising a plurality of panels disposed in vertical alinement, each consisting of a skeleton frame the sides of which removably engage the sides of adjacent frames, foraminous sheetings secured along their marginal portions to the opposite sides of said frame and a homogeneous mass of substantially chemically inert, non-hygroscopic, incombustible, shock resistible fibrous material uniformly filling the area between said sheetings for absorbing sound, an inverted U-shaped member fixed to said ceiling and telescopically fitting over the upper side of the frame for the upper panel, and means for detachably connecting said U-shaped member to the frame of the upper panel.

3. In testing apparatus, the combination with a structure having a support and spaced side walls, of a battery of units on said support between said side walls and disposed side by side in spaced relation to form flow paths for a sound carrying medium, each unit comprising a plurality of panels disposed in vertical alinement and each consistin of a skeleton frame the sides of which removably engage the sides of adjacent frames, foraminous sheetings secured along their marginal portions to the opposite sides of said frame and a homogeneous mass of substantially chemically inert, non-hygroscopic, incombustible, shock resistible fibrous material uniformly filling the area between said sheetings for absorbing sound, a nose member removably secured to the sides of the frames at the leading end of each unit, and a tail member removably secured to the sides of the frames at the opposite end of each unit and terminating in convergin walls.

4. In testing apparatus, the combination with a structure adapted to form a chamber for the device to be tested and having side walls forming an exhaust opening, of a battery of sound absorbing units mounted in said exhaust opening, said battery of units consisting of inner and outer series of vertical panels, the panels of the in-' ner series being disposed parallel to each other and the side walls forming said exhaust opening and the panels of the outer series being parallel to each other but disposed at an angle to the panels of the inner series, and separate horizontally disposed sound absorbing panels spaced one above the other and spannin the spaces between the panels of one of the first mentioned series of panels.

5. In testing apparatus, the combination with a structure having a support and spaced walls forming an opening, of a battery of sound absorbin units in said opening disposed side by side in spaced relation to form flow paths for a sound carrying medium, each unit comprising a series of panels supported one on another in vertical alinement, each panel consisting of a skeleton frame having upper and lower U-shaped channel members, the side walls of which extend outwardly, the side walls of the lower channel member of each frame being supported on corresponding wall of the upper channel member of the adjacent lower frame, foraminous sheetings secured along their marginal portions to the op- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,073,951 Servais Mar. 16, 1937 ,101,460 Schmidt Dec. 7, 1937 2,152,169 Appel Mar. 28, 1939 2,160,001 Saborsky May 30, 1939 2,270,825 Parkinson et a1. Jan. 20, 1942 2,281,963 Van Tongeren May 5, 1942 

